Field of the Invention
The present invention relates to an imaging optical system and a reading apparatus including the same, and more particularly, to a reading apparatus capable of conducting reading with high resolution even in a compact size and an imaging optical system included in the reading apparatus.
Description of the Related Art
Hitherto, there has been known a reading apparatus configured to read an object from above.
In U.S. Patent Application Publication No. 2010/0097582, there is disclosed a reading apparatus including a curved mirror and a plurality of lenses.
Further, in U.S. Patent Application Publication No. 2010/0097582, in order to enable the reading apparatus to conduct reading with high resolution even in a compact size, a ratio between a distance from a curved mirror surface arranged closest to the object side to an image pickup element surface and a distance from an optical axis of a plurality of lenses to an edge part of the image pickup element surface which is farthest from the optical axis is defined in an optical system included in the reading apparatus.
However, in U.S. Patent Application Publication No. 2010/0097582, the above-mentioned ratio is set to be larger than 20. Therefore, when a large-sized image pickup element is used for the reading apparatus disclosed in U.S. Patent Application Publication No. 2010/0097582, the entire length of the optical system needs to be increased, and hence there arises a demand for an increase in size of the reading apparatus.